1. Field of the Invention
The invention relates to the detection of a predetermined pattern in a serial stream of binary data.
2. Discussion of the Related Art
In the field of binary data transmission, data may be serially transmitted one bit at a time along a transmission path. Often the serial data is transmitted by frames which are delimited by codes used to identify the beginning or end of each frame. Such codes must be identified in the data stream before the significance of the data in the frames can be determined.
More particularly, a standard H261 in the field of transmission of compressed image data over telephone networks determines that such data is to be transmitted in frames of 512 bits. The first bit of each frame is a synchronization bit and the synchronization bits of twenty four consecutive frames constitute a predetermined synchronization word or a cyclical permutation thereof. This twenty four bit word is in fact an eight bit word, repeated three times. A series of eight such consecutive frames is known as a multiframe.
German patent application number 36 23 910 describes a method comprising the steps of storing each incoming bit in a memory comprising groups of words, each group of words having at least l bits, such that each group of words contains bits from a same position in consecutive frames. Each group of words is rotated and compared, at each rotation, to the synchronization word. The method is carried out by a microprocessor to achieve bit by bit writing to the memory, which is complex.
An object of the present invention is to detect, in a simple manner, a synchronization word in a stream of serial data transmitted by frames, the synchronization word comprising several bits, transmitted one bit per frame.